In the electronics and microelectronics field it is common to use a step of bonding two substrates together. This type of bonding is for example used to fabricate SOI (silicon-on-insulator) substrates or for 3D integration of substrates comprising electronic circuits that are to be connected.
It is generally necessary to evaluate the bond quality which is characterized in particular by the adhesion energy, also called the bonding energy, of the bond between the surfaces of two substrates.
Various metrology processes have been proposed in the prior art for characterizing this adhesion energy.
A traction-test process is known from the prior art, this being a process for determining the adhesion energy directly and macroscopically. However, this process is very difficult to implement.
A bond measurement process, proposed by Maszara in the document entitled “Bonding of silicon wafers for silicon-on-insulators”, J. Appl. Phys. 1988, 64, 4943, is also known.
In this process, a blade is inserted at the bond interface between the two substrates. Applying a mechanical force via the blade in a direction parallel to the plane of the bond interface causes the two substrates to debond locally and the debonded region to propagate over a certain distance. The length over which the debonded region has propagated gives an indication of the energy of adhesion between the two substrates.
However, this process has several drawbacks.
This process is an indirect measurement of the adhesion energy since it is extrapolated from the propagation of the interface debond. The quantity measured is therefore the tear strength of an interface rather than the adhesion energy itself.
Furthermore, this process is dependent on the blade insertion conditions and on the operator, which make it an imprecise process.
In addition, this process is macroscopic, that is to say that it allows only an average adhesion energy to be determined over a significant area, rather than a local adhesion energy.
Finally, this process is implemented at room temperature and therefore characterizes the adhesion energy only at room temperature.
It is therefore clear that the processes of the prior art for measuring an adhesion energy have numerous drawbacks.